Adulterants
Because of its extreme cheapness and potency, the purity of LSD in blotter form is not an issue: either it's lsd or untreated paper. The purity of powders, pills, and liquids cannot be assumed as safe....If there are 200 micrograms of LSD in a tablet, there could only be 200 mics of impurities present even if the LSD was originally only 50% pure (assuming nothing else has been added), and few compounds will produce a significant effect until a hundred to a thousand times this amount has been ingested.

L = pounds (the "L" comes from the Latin word for pound,
libra, and a pound sign "£" is still a stylised L)S = shillingsD = pence (the "D" again comes from Latin, this time from
the word denarius which was a unit of currency in the Roman Empire)

Hence there were 240 pennies in a pound. Just to confuse things further there
were a number of other nicknames for various amounts of currency which were
in common use (much like dime and nickel are used in modern USA).

Anything you see on an acid trip, anything you think, is entirely a result of you. You will think about things you normally think about. You will see things you normally see. The difference between an acid trip and normal thought is not that great. It's not a magical chemical that will hook you into the collective unconscious, because if there is one, you're going to have to sober up a little to find it.

A small tasteless
White tab
Drops on my tongue.
Causes colors to live
Inside my head.
Makes crucifixes
Of tree branches.
Sends fires tentacles
Reaching for me to burn
And sear and saute my skin.
I like these little white tabs.
They make everything right.

One of the greatest questions about LSD is whether or not it causes hallucinations. While this may seem to be like asking whether rain causes things to be wet, it is not as simple as all that.

The consensus amongst The Merck Manual, alt.drugs.psychedelics and people I have talked to, is that LSD very rarely causes actual hallucinations. While the hallmarks of an acid trip include distortions of space and time, bright colors, and the feeling that inanimate things are moving; actual full on visuals of things that are not there is fairly rare for people who have taken LSD. A rough estimate that I was given on usenet is that less then 5% of LSD trips involve such appearences.

As for what caused LSD, when it was first became popular in the 60's, to be popularly known as a drug that caused hallucinations, the answer may lie in a good amount of media hysteria surrounding it, or in the fact that doses of the drug were much higher at the time, up to 100 micrograms per tab. In any case, unless someone is already mentally ill, or they are taking a lot of very strong, pure LSD, the chances that they will see full visuals of non-existent things is, supposedly, very slim.

Due to personal experience with LSD and based on my training in cognitive psychology, I hypothesize that LSD disrupts iconic memory, i.e. the visual mode of sensory memory, because, in the widely accepted information-processing system models of cognition, sensory memory is the next stage of processing after sensory input. Iconic memory retains information for between 0.5 and 1.0 second, whereas echoic memory, the auditory mode sensory memory, lasts between 3.0 and 4.0 seconds, just long enough for working memory to grab hold of salient information. In particular, working memoryrecognizes patterns and feeds distilled information to long term memory where comprehension processes take over (i.e. the lexicon in the case of reading). Regardless of whether attention is the result of bottom-up or top-down phenomena (or both), sensory memory is a constantly renewed copy of low level perception.

Photographic memory occurs when iconic memory is precisely tuned and orderly to the extent that incoming visual stimuli do not rapidly decay. As to what this mechanism must be like, it does not employ afterimages or normal mental imagery. The human visual system is "hard wired" at infancy, and there is no hope for the full recovery of visual perception, as stated earlier. Also, considering that occular dominance columns must develop before a critical age, it is clear that the foundation the visual system does not deal very well with insult. Concerning the gradual extinction of visual tracers, this is probably due to attentional compensation provided through working memory, and is not the result of an increase in available visual information.

After using LSD, the representation of a visual stimulus in iconic memory is no longer governed by precise neuronal firing patterns, but is rather subject to whatever alterations has LSD wrought. LSD is not neurotoxic, yet it does alter synaptic configurations. In the early visual pathway, these changes are not readily reversed. Thus, as goes the early visual pathway, so goes the quality of information in iconic memory. Just as a photograph's detail is limited by the lens, so to is the detail of a memory limited by perceptual fluency. In conclusion, you can kiss your perfect photographic memory good bye forever the first time you take LSD!

LSD is also an abbreviation for Long Slow
Distance, a method of running known for its relaxed and gentle approach to training.

The concept originated in the 1920's with Arthur Newton, a British marathoner living in South Africa. Dissatisfied with the training philosphies of his time which stressed fast running over short distances, Newton began running longer and longer distances at a more relaxed pace.

Newton had won the 1922 55-mile Comrades Marathon in 8:40. Using his new approach and running roughly 17 miles a day six days a week, he crushed this personal best, breaking the seven-hour barrier in 6:56.

Long slow distance was popularized in 1969 by former Runner's World magazine editor Joe Henderson in his books Long Slow Distance: The Humane Way to Train and The Long Run Solution. (The latter is one of the few books I
would enter a burning house to retrieve.)

Henderson maintains that LSD is not so much a training method as it is a way to enjoy running. The easy, stress-free daily run is an end in itself. Hop out of bed, step into running shoes, head out the door for the better part of an hour and feel a gazillion times better, at least fully awake.

I then noticed that the mist rose also from me. It danced with the constant outward breath of every living thing around me. As I inhaled, I absorbed it. As I exhaled, it absorbed me. The division between me and the universe disappeared. My skin turned to vapor then vanished in a breeze.

Electric and naked, I bounded through fields a thousand yards at a time. Rain fell from leaves like crystal kisses from loving tongues as I broke more trail and found myself back on the road. It took me an hour at a good but effortless pace to get back home, the sun in the trees pouring gold on to
puddles.

When I stopped in front of my house, my wife and new baby snoozing inside, I felt as if I had returned from an enlighteningtrip. My body hummed, each muscle simultaneously felt stressed and massaged. My mind swam with the effects of a few hours on the roads. I got a few gulps of water from
the hose. Three herons glided across a fading eastern sky, and I could not help laughing.

The neurochemistry of LSD - A technical explanation
for nontechnical readers.

The primary effect of LSD occurs at receptors
intended to respond to serotonin (kudos
to enth for touching on this in the most
detail so far). Serotonin (aka 5-HT, 5-hydroxy
tryptophan) exists as an evolutionarily new
addition to our brains. All the highest systems
make heavy use of it, including our frontal lobe
(and specifically, the prefrontal cortex) that
seems to give us an edge (intelligence-wise)
over every other animal on Earth. It also has
effects outside the brain, which happens to
(partially) explain why LSD causes things like
jaw clenching and nystagmus. Believe it or
not, LSD has more effect on smooth muscle
tissue than it does in the brain.

To get right to the point, LSD acts as a
5-HT2 partial agonist (the
"2" just designates a particular
type of postsynaptic receptor).
This results in a decrease in the amount of
serotonin that gets dumped into a synapse,
but at the same time LSD produces some degree of
effect similar to serotonin itself.

Of course, keep in mind that the previous paragraph
only describes the best current theory, in that it
most fully accounts for LSD's effects at the local
level of an actual synapse. A good site with some
alternative theories as to its actual action in
a serotonergic synapse lives at
"http://www.cs.hmc.edu/~ivl/writing/non_fiction/lsd/".
(I apologize for the external link, but I have
yet to find a better site discussing the specifics,
including competing theories, of the activity of
LSD at the synaptic level).

So what does serotonin actually do...

It acts to prevent the postsynaptic cell
from firing (ie, it acts as an "inhibitory"
neurotransmitter). So, decreasing serotonin
release into a synapse increases the rate of
firing of the postsynaptic cell. Thus, LSD
"speeds up" the outer layer of the brain. This
doesn't mean you think faster (and
certainly not "better"), just differently.

Now that you have that down...

LSD also acts at noradrenergic synapses, though
its effect on such sites has received far
less research than its effects on serotonergic
receptors. I'll focus on the main system affected
here, rather than the specific receptors, for that
reason.

The Locus Coeruleus, which communicates primarily
using norepinepherine (thus the connection with LSD)
acts as the "gate" for letting sensory input get
through to the parts of us we consider "us" .
most of the time, it filters out the vast
majority of information we receive, but LSD forces
it open, so we become aware of countless features
of our environment we normally don't notice. On
the down side, LSD also garbles the transmission,
leading to the cross-modal experiences one
can sometimes experience while tripping (such as
"hearing" a color, a classic effect of LSD that most
users describe as not really occuring to such an
obvious degree).

To summarize, LSD temporarily modifies the way
we consciously process information. At the
same time, it gives us conscious access to
immensely more information, though not reliably
true information, than we normally perceive.

The abbreviation LSD, commonly used, refers to the molecule LSD-25, or lysergic acid diethylamide. This LSD was first synthesized in the mid-20th century and is known for its effect in producing changes in sensation, perception, and consciousness in humans. This effect has been alternately described as psycholytic, psychedelic, psychomimetic, hallucinogenic, or entheogenic, depending on the age, the describer, and the framework in which they are analyzing it.

In structure, affective mechanism, effects, and use, LSD is similar in some degree to psilocyn, psilocybin, and mescaline, although it is different from these substances and most other pharmaceuticals of all kinds in that it produces effects at very low dosages, its influence noticeable in humans at the high two-digit microgram range. LSD is used for psychiatric, religious, and recreational purposes, though it is best known for the latter, and while most experts who have studied it believe it to have no immediate or long-term negative physical effects, fears of psychological damage and social and political concerns have lead to the criminalization of its manufacture, sale, possession, and/or consumption in many areas worldwide.

LSD was originally produced in 1938 by the chemist Albert Hofmann at the German company Sandoz Pharmaceuticals, in the course of a study of alkaloids found in the grain fungus ergot. Ergot had long been known as a poison which induced symptoms, collectively known as ergotism or "Saint Anthony's Fire", which included hallucinations and severely altered mental states. Ergot had also, however, proven useful as a source of folk medicine for use in childbirth, and in the 1930s chemists began to learn about ergot alkaloid structures (all shared a core of lysergic acid) and produce ergot derivatives, principally ergotamine, which were found to have marketable medical applications.

Lysergic acid diethylamide was Hofmann's 25th lysergic acid derivative, and the rest of its anglophonically unintuitive abbreviation is accounted for by the fact that it was given the German appellation of "lyserg saure diathylamid". On the basis of similarity to other diethylamides, LSD was expected to have analeptic (respiratory and circulatory stimulant) properties. Animal testing, however, did not indicate much promise as a pharmaceutical product, though the test subjects were noted to show some signs of restlessness and agitation.

The effects LSD is now principally known for were not discovered until 1943, when Hofmann, believing it would yet show some usefulness, synthesized another batch and in so doing apparently came into contact with the substance, which was absorbed transdermally, through the skin. Hofmann's synthesis was "interrupted by unusual sensations", and he returned home, reporting restlessness, dizziness, and the experience of seeing a dreamlike play of pictures, shapes, and colors with his eyes closed.

Three days later, to confirm his suspicion that this experience was a product of LSD, he intentionally ingested a quarter of a milligram (an amount roughly equal to two to four modern-day "hits" of the drug), and experienced delirium, strange and threatening changes in the visual appearance of physical objects and in his perception of time, disassociation, and a sense of his impending death, part of what would now be considered a "bad trip", surely aggravated by his complete unawareness of any precedent for this effect. A doctor his assistant summoned reported no apparent physical effects, however, and the symptoms eventually faded to a pleasant synaesthesia before ultimately disappearing and leaving behind no ill effects.

Hofmann's experiences proved replicable, and further study into the effects of LSD and related compounds was conducted. The possible market for such a drug was not immediately apparent, but it was soon seized upon by psychiatrists, who used it in attempts to understand the viewpoint of the schizophrenic or otherwise mentally atypical patients they worked with. Some of these professionals later found it more useful when administered to patients in conjunction with talk therapy, a strategy many therapists found useful in reducing inhibitions, producing revelations and breakthroughs in self-awareness, and in assisting patients in addressing traumatic or repressed memories and events from their past. Sandoz was more than happy to service this market, distributing LSD under the brand name Delysid.

LSD was also early on seized on for its possible religious significance, encouraged by contemporary interest spurred by Aldous Huxley, R. Gordon Wasson, and others in the role of mind-affecting fungi, peyote, and similar substances in the shamanic religions of ancient Europe, India, and the native peoples of America. The use of LSD in a religious context was not limited to animistic traditions, however. Al Hubbard, a maritime entrepreneur with an unusual background, strongly promoted its use in the context of Catholicism, sparking some interest in the church in western Canada, while Walter Pahnke's "Good Friday Experiment" indicated the usefulness of the similar psychedelic psilocybin in producing transcendent religious experiences among a group of Harvard Divinity School students.

The United States government also took interest in LSD, investigating its effects and possible uses, most famously as a possible truth serum and mind control agent in the MKULTRA tests, a purpose for which it was ultimately deemed unsuitable. Though it made use of such unscrupulous methods such as administration to subjects without informed consent, including subjects who did not even know they were part of a test at all, the government also conducted standard experiments for which it recruited volunteers from academia. Between these tests, similar experiments carried out by private research institutes, the use of LSD in psychiatric therapy, and later self-administration outside of an institutional context, a significant amount of the United States intelligentsia first encountered LSD, either through direct experience or secondhand accounts, in the 1950s and 1960s.

Though growing awareness of the drug by way of dissemination downwards from the intellectual class and upwards from the popular media accounts of LSD research meant that its introduction into the mainstream culture was more or less inevitable, this process was immeasurably hastened by Harvard psychology professor Timothy Leary. After encountering psilocybin in Mexico in 1960, Leary began to work with LSD, for which he became a fierce evangelist, first privately and soon publicly, continuing after his dismissal from Harvard in 1963. Simultaneously, the demand for LSD in quantities greater than official sources were capable of — or willing to — supply inspired independent producers, most famously Owsley Stanley, to manufacture their own LSD, motivated by profit or philosophy.

Even this, by itself, might not have prevented the successful integration of LSD into western culture. But, in one of those coincidences of history, these developments occurred simultaneously with the emergence in America of a strong youth and dissident subculture, itself the product of several cultural trends converging - reaction against the Cold War in general and the Vietnam War in particular, high tensions over civil rights and the role of women and minorities in America, uneasiness originating in the further shift from an agricultural to an industrial economy and the development of consumerism, and the latest incidence of the recurrent utopianism, frequently associated with strong but nontraditional spiritualism, free love, communal living, socialism, and withdrawal from the mainstream culture, that has periodically arisen every few decades in America since at least as far back as the early 19th century. Many members of this subculture, which tend to get labeled with the catchall appellation of "hippies", embraced LSD for spiritual and recreational purposes, integrating its use as an important, if not fundamental, aspect of their identity and lifestyle.

The dominant culture, left fairly unsettled by the aforementioned trends itself and rendered severely apprehensive or outright fearful about this subculture, found in LSD at least one thing it could take direct action against, and prohibited it at first the state, and then the national level in the mid-1960s. In fairness, it should be noted many citizens were truly fearful of yet unknown and possibly damaging long-term effects of LSD use, though these concerns are generally thought to have been exaggerated by sensationalistic press and government treatment more concerned with public order. Other governments, urged on by the United States and fearful that it would contribute to similar conditions of domestic unrest, followed suit.

Despite its prohibition, LSD proved rather popular as a recreational drug throughout the 1960s and 1970s. Since then its use has by no means disappeared, though it has decreased and become less prominent in response to long-term cyclical trends in drug use and the introduction of new drugs like Ecstasy (MDMA). Ecstasy, of course, after proving useful in psychiatry merged with youthsubcultures in 1980s England in a manner quite similar to LSD's American experience. The "serious" work of studying LSD and its uses in religious and psychiatric contexts has to a large part been collateral damage, facing significant government-imposed barriers, but researchers have recently made some headway in this regard. Many speculators hope that with the passage of time creating a distance from the tensions surrounding its original introduction into the general society and a growing willingness among western nations to reassess their policies on recreational drug use, LSD may yet be integrated into mainstream culture.

References:
Albert Hofmann - LSD - My Problem Child
Jay Stevens - Storming Heaven: LSD and the American Dream
Martin A. Lee & Bruce Shlain - Acid Dreams: The Complete Social History of LSD: The CIA, the Sixties, and Beyond
Some information probably originally from Lycaeum (www.lycaeum.org), Erowid (www.erowid.org), and the Multidisciplinary Association for Psychedelic Studies, it's been a while.

Many people experience back aches during or after an acid trip. This is the basis of the infamous myth that LSD stays in your spine and causes flashbacks. Pure LSD will, in fact, not cause this phenomenon. The back aches are caused by the vascular-constrictive (constricting of blood vessels) properties of the various other amides of lysergic acid that will undoubtably be found in street acid. LSD is nearly impossible to synthesize and it is also nearly impossible to obtain pure ergotamine tartarate, from which LSD is made. Furthermore it is a very fragile molecule. It can be broken down by light or in the presence of strong acids or bases. This happens when a water solution of LSD crystals is futher dilluted by a dope peddeler with chlorinated tap water or applied to treated "blotter" paper. Some of the amides that it breaks down into are still psychoactive (although not to the same degree) but they have been blamed for many of the side effects.